Fuel-cell assembly comprising an electrolyte reservoir

ABSTRACT

The invention relates to a fuel-cell assembly comprising a number of fuel cells ( 12 ) that are arranged in a stack ( 10 ). Each fuel cell contains an anode ( 1 ), a cathode ( 2 ) and a porous electrolyte matrix ( 3 ) arranged therebetween. An electrolyte reservoir ( 11 ), which compensates the electrolyte losses from the fuel cells ( 12 ) is provided at the end, or in the vicinity of the end of the fuel cell stack ( 10 ), said electrolyte being transported to the individual fuel cells ( 12 ) by electrical forces within the fuel cell stack ( 10 ). According to the invention, the electrolyte reservoir ( 11 ) is configured as a supporting structure which forms hollow chambers that contain porous bodies for absorbing the electrolyte in their pores.

[0001] The invention relates to a fuel cell assembly pursuant to thepreamble of claim 1.

[0002] We know of fuel cell assemblies, especially assemblies of moltencarbonate fuel cells, where a number of fuel cells, which each containan anode, a cathode and a porous electrolyte matrix arranged betweenthem, are arranged in the form of a fuel cell stack.

[0003] In molten carbonate fuel cells, mixtures of alkali carbonates areused as electrolyte, causing the fuel cells to be liquid at theoperating temperature. The electrolyte is contained both in the porouselectrolyte matrixes and in the anodes and cathodes of the fuel cells,which are likewise made of porous material, and is kept there withcapillary force. The function and efficiency of a molten carbonate fuelcell are dependent upon the complete and correct filling of theelectrolyte, which is accomplished during manufacturing by adhering totight tolerance settings. Both over-filling and under-filling withelectrolyte negatively influence the efficiency and durability of thecells.

[0004] During fuel cell operation, parts of the electrolyte contained inthe cells are lost due to various mechanisms, of which the following areessential:

[0005] due to the strong wetting property of the molten alkalicarbonates, the electrolyte has the tendency of creeping out of the cellin the fringe area and on the orifices that are provided for supplyingand removing fuel gas and oxidation gas, wherein it then spreads to theexterior surface of the fuel cell stack and the adjacent components;

[0006] the alkali carbonates of the electrolyte enter into chemicalreactions with construction materials of the fuel cells, wherein aportion of the electrolyte is bonded with the resulting chemicalcompounds; and

[0007] constituents of the alkali carbonates bond with water, which iscreated in the fuel cells as a reaction product, to form hydroxides,which evaporate at the operating temperature of the fuel cells.

[0008] The gradual electrolyte loss during the life of the fuel cellleads to a decrease in power and may possible represent a factor thatlimits the life of the fuel cell.

[0009] One possibility for overcoming the above-mentioned difficultiesis to provide an electrolyte reservoir to compensate the electrolytelosses from the fuel cells.

[0010] For example we know from DE 195 45 658 A1 of a molten carbonatefuel cell where a porous body with an electrolyte supply is provided inat least one place to compensate electrolyte losses. This porous bodyforming the electrolyte supply is assigned to the individual fuel cell;in a fuel cell assembly comprising a number of fuel cells arranged inthe form of a stack thus each individual fuel cell would be providedwith such a porous body for maintaining a supply of electrolyte.

[0011] From JP 61074265 A we know of a matrix configuration for a fuelcell where the electrolyte is being distributed in the matrix from anelectrolyte reservoir that is assigned to the matrix in order tocompensate losses. Here as well, in the case of a fuel cellconfiguration comprising a number of fuel cells that are arranged in theform of a stack each matrix of the individual fuel cells would beequipped with such an electrolyte reservoir.

[0012] Further suggestions in which each individual fuel cell should beequipped with electrolyte reservoirs for compensating electrolyte lossesare known from U.S. Pat. Nos. 5,468,573, 4,185,145, 4,548,877 and JP61277169 A.

[0013] Furthermore we know from U.S. Pat. No. 4,467,019 and JP 07326374A of fuel cell assemblies with several fuel cells that are arranged inthe form of a stack, where the electrolyte matrix of each fuel cell,respectively, is connected with an electrolyte reservoir that isprovided outside the fuel cell stack for the purpose of compensatingelectrolyte losses that occur.

[0014] Finally we know from U.S. Pat. No. 4,761,348 of a fuel cellassembly where on the ends of the fuel cell stack, respectively,electrolyte reservoirs—one with an excess of electrolyte and one with alack of electrolyte—are provided, which are separated from the completecells of the stack by impermeable, yet electrically conductiveseparators, but are subjected to an electrolyte exchange with the fuelcells.

[0015] The existing solution suggestions have many disadvantages. In thecase of individual electrolyte reservoirs that are provided in each fuelcell only a limited amount of electrolyte can be maintained unless aconsiderable increase in volume and cost of the cells is acceptable. Inthe case of devices for filling the electrolyte supply in the individualcells it is very difficult to distribute the replenish quantity exactlyamong the individual cells within the stack and fill each individualcell correctly. Channels or lines for filling the electrolyte form pathsfor parasitic currents along the fuel cell stack, which can reduce thepower of the fuel cell assembly and even destroy it.

[0016] Another difficulty in connection with the loss and replenishingof electrolyte for fuel cells that are arranged in a stack consists ofthe fact that the electrically charged particles of the electrolytemigrate in the direction of the opposite polarity under the influence ofthe electric field that is generated by the fuel cell tension along thestack. The alkali ions contained in the electrolyte therefore have thetendency of migrating from the positive end to the negative end of thefuel cell stack under the influence of the electric field. Thus, therate of electrolyte loss in the cells on the positive end of the fuelcell stack is considerably higher than that of the cells on the oppositeend. With constantly maintaining or replenishing electrolyte for allcells the cells would become overfilled in the vicinity of the negativeend of the fuel cell stack and those on the positive end would not befilled sufficiently.

[0017] It is therefore the object of the present invention to create animproved fuel cell assembly comprising an electrolyte reservoir.

[0018] This task is resolved with a fuel cell assembly with the featuresof claim 1.

[0019] Beneficial further developments of the fuel cell assemblypursuant to the invention are described in the dependent claims.

[0020] The invention creates a fuel cell assembly comprising a number offuel cells that are arranged in the form of a stack, wherein each cellcontains electrodes in the form of an anode and a cathode and a porouselectrolyte matrix arranged between them, as well as a current collectorfor contacting the electrodes, and wherein furthermore an electrolytereservoir for compensating electrolyte losses from the fuel cells isprovided. Pursuant to the invention, the electrolyte reservoir isarranged on or in the vicinity of an end of the fuel cell stack, whereinthe electrolyte is transported to the individual fuel cells byelectrical forces within the fuel cell stack, and wherein hollowchambers, which are formed by a supporting structure and which containporous bodies absorbing the electrolyte in the pores, serves as theelectrolyte reservoir.

[0021] A considerable advantage of the fuel cell assembly pursuant tothe invention is that under the effect of the electrical forces actingin the fuel cell stack the electrolyte is supplied automatically tovarious positions within the stack while being adapted to the differentelectrolyte loss rates. Another benefit is that the invented fuel cellassembly is easy and inexpensive to manufacture and easy to operate.Another advantage consists of the fact that due to the lack of lines orchannels along the fuel cell stack for distributing the electrolyte fromthe outside among the individual fuel cells paths for disadvantageousleakage currents are eliminated. Since the electrolyte reservoircontains a supporting structure, it is not required that the material,which absorbs the electrolyte directly, assume the supporting function.The appropriate material is therefore mechanically relieved, which isbeneficial with regard to its creep stability.

[0022] The electrolyte is preferably one component of a spreadable orflowing paste, which is introduced into the hollow chambers of thestructure, wherein additional components of the paste after curingcreate a porous body whose pores contain the electrolyte. The supportingstructure could be for example a current collector, which is installedon the positive end (in fuel cells the cathode) between the end plateand the last cell. Similarly also a large-pored foam structure can beprovided as the supporting structure, where the pores are filled withpaste. Alternatively the paste can be introduced into recesses or boreholes of the end plate so that the end plate itself serves as thesupporting structure of the electrolyte reservoir.

[0023] Pursuant to another beneficial aspect of the invented fuel cellassembly the electrolyte reservoir is installed on one end of the fuelcell stack and an electrolyte-absorbing reservoir in the form of aporous body for absorbing excess electrolyte is provided on the otherend of the fuel cell stack. This way, due to the migration ofelectrolyte from the electrolyte reservoir to the other end of the fuelcell stack, too much electrolyte that may be occurring is removed overtime. The porous body for absorbing excess material can be designedaccordingly like the electrolyte reservoir, with the correspondingbenefits.

[0024] The electrolyte reservoir is preferably installed on the positiveend of the fuel cell stack, and the electrolyte-absorbing reservoir forabsorbing excess electrolyte is provided on the negative end of the fuelcell stack.

[0025] Pursuant to a beneficial development of the invented fuel cellassembly the electrolyte reservoir can be filled. Electrolyte lossesoccurring during operation of the fuel cell can thus be compensated sothat a continuously optimal operation of the fuel cell assembly isfeasible.

[0026] Preferably an electrolyte filling line, which is connected withthe electrolyte reservoir and extends from the fuel cell stack to theoutside, for filling the electrolyte reservoir from the outside isprovided.

[0027] A preferred embodiment provides for the electrolyte filling lineto have a vertical or outwardly ascending course.

[0028] Pursuant to a particularly beneficial embodiment of the inventedfuel cell assembly, the electrolyte filling line is provided for fillingthe electrolyte, which exists in solid form at ambient temperature,preferably in the form of pellets, wherein the solid electrolyte at theoperating temperature melts in the fuel cell stack and is received bythe electrolyte reservoir.

[0029] As already presented above, the electrolyte reservoir consists ofa porous body, whose pores are filled with the electrolyte. The poresize of the electrolyte reservoir is preferably larger than that of thepores of the electrolyte matrix. This way capillary forces support thetransport of electrolyte from the reservoir to the matrixes of the fuelcells.

[0030] Pursuant to a preferred embodiment of the invented fuel cellassembly the porous body of the electrolyte reservoir consists of fuelcell cathode material that is completely impregnated with electrolyte.

[0031] Pursuant to another preferred embodiment of the invented fuelcell assembly it is provided that the supporting structure of theelectrolyte reservoir consists of an electrically conductive material,which serves as the electrical connection between the last fuel cell andthe end of the fuel cell stack.

[0032] Pursuant to a beneficial embodiment of the invented fuel cellassembly it is provided that along the fuel cell stack betweenindividual components of the fuel cells and/or the fuel cell stackexisting capillary travel paths for the electrolyte are designed withregard to their thickness and/or their pore size such that anoptimization of the electrolyte transport within the fuel cell stackfrom the electrolyte reservoir to the fuel cells takes place. This waythe speed of transport and the type of distribution of electrolytedelivered from the electrolyte reservoir to the individual fuel cellscan be optimized.

[0033] Pursuant to another preferred embodiment of the invented fuelcell assembly, means for monitoring the tension of the most positivefuel cell or a group of most positive fuel cells are provided and adecrease in this tension is used a signal for filling the electrolytesupply in the electrolyte reservoir. Since due to the electrical forceswithin the fuel cell stack the electrolyte loss of the fuel cells ishigher the higher these forces are on the positive end of the fuel cellstack, the tension of one or more fuel cells on the positive end of thestack is a reliable signal for the necessity of replenishing theelectrolyte supply.

[0034] Finally, pursuant to another beneficial aspect of the inventedfuel cell assembly, it is provided that the electrolyte in theelectrolyte reservoir is filled in a composition that differs from theinitial composition of the electrolyte in the electrolyte matrixes ofthe fuel cells in order to compensate disproportionate electrolytelosses during the fuel cell operation. The electrolyte that is used forfilling the electrolyte reservoir therefore contains those componentsthat are lost at a higher rate during operation in higher concentrationsthan would correspond to the initial or normal composition of theelectrolyte in the electrolyte matrixes.

[0035] The following describes examples of embodiments of the inventedfuel cell assembly based on the drawing:

[0036]FIG. 1 shows a diagrammatic perspective exploded view of a fuelcell assembly with fuel cells that are arranged in the form of a stackpursuant to an example of the invention, wherein for the purpose ofbetter clarity only a few of the fuel cells that make up the fuel cellstack are depicted;

[0037]FIG. 2 shows an enlarged side cross-sectional view of a currentcollector, in whose hollow chambers pursuant to another preferredexample of an embodiment of the invention the electrolyte reservoir isprovided with a porous body for absorbing excess electrolyte.

[0038] In FIG. 1 the reference number 10 designates a fuel cell stack,which consists of a number of fuel cells 12, which each contain an anode1, a cathode 2 and an electrolyte matrix 3 arranged between them.Adjacent fuel cells 12 are separated from each other by a bipolar plate4 and adjoining current collectors 17, which serve the purpose ofguiding the currents of a fuel gas B and an oxidation gas O separatelyvia the anode 1 or via the cathode 2 of the fuel cells, wherein theanode 1 and the cathode 2 of adjacent fuel cells are separated from eachother from a gas engineering point of view by the bipolar plate 4. Thecurrent collectors 17 ensure electrical contacting of the cells amongeach other.

[0039] The fuel cell stack 10, which contains a variety of such fuelcells 12, of which however only a few are shown in the figure forclarity reasons, is closed on its top and on its bottom, respectively,by an end plate 6, 7, wherein these end plates 6, 7 are connected witheach other by rods 5 and are tensioned in relation to one another sothat the individual fuel cells 12 are held against each other at aspecified pressing force. On the exterior sides of the fuel cell stackgas distributors 14 are provided, which are sealed against the fuel cellstack 10 by gas distributor gaskets 15 and serve the purpose of feedingand removing currents of fuel gas B and oxidation gas O. For clarityreasons only one such gas distributor 14 including the gas distributorgasket 15 is shown in the figure.

[0040] On the upper end of the fuel cell stack 10, which correspondingto the orientation of the fuel cells 12 in relation to the position oftheir anode 1 and cathode 2 is the positive end of the fuel cell stack10, an electrolyte reservoir 11 is arranged, which is located betweenthe uppermost, i.e. the most positive fuel cell 12 and the upper endplate 6 of the fuel cell stack 10.

[0041] The electrolyte reservoir 11 consists of a supporting structure,in whose hollow chambers porous bodies 16 are arranged, the pores ofwhich are filled with the electrolyte. The electrolyte is transportedfrom the electrolyte reservoir 11 by electrical forces within the fuelcell stack 10 to the individual fuel cells 12 in order to compensate theelectrolyte losses occurring there. In detail this takes place such thatduring operation of the fuel cell assembly the electrolyte, i.e. theions contained in it, migrate via capillary paths or surface paths fromthe positive to the negative end of the fuel cell stack under theinfluence of the electric field existing within the fuel cell stack. Thepaths can e.g. be on gasket surfaces with external gas distributors orthe surfaces of gas distribution channels within the stack in the caseof a fuel cell assembly with internal gas distribution.

[0042] The supporting structure is preferably a current collector 4 a,which is arranged between the end plate 6 and the last fuel cell 12 ofthe stack. Alternatively the supporting structure consists of structuralfoam with macro-pores. A paste, which can be cast or spread, is filledinto the hollow chambers of the current collector or structural foam.The paste consists of powdery starting substances, which are mixed witha liquid binding agent. A curing process creates a porous body 16, whosepores hold the electrolyte.

[0043] The pore size of the porous body 16 holding the electrolyte islarger than the size of the pores of the electrolyte matrix 3 of thefuel cells so that due to the ratio of the capillary retaining forces,which act upon the electrolyte, between the electrolyte reservoir 11 andelectrolyte matrixes 3 of the fuel cells 12 the electrolyte, migratingalong the fuel cell stack 10, will have its source in the electrolytereservoir 11 instead of in the active fuel cell components. On the otherhand, due to the capillary forces, any deficiency of electrolyte in thematrixes and/or electrodes of the fuel cells will be filled from thesmall, yet constant electrolyte quantity migrating from the electrolytereservoir 11 until all small pores of the matrix 3 and/or the electrodes1, 2 have been filled.

[0044] The porous body 16 of the electrolyte reservoir 11 consistspreferably of the material of the fuel cell cathodes, which iscompletely impregnated with electrolyte. The porous body 16 can also beinserted or filled into the hollow chambers in the form of cured moldedpieces. Preferably however a paste-like mass is inserted, which whenexposed to air cures within a short period of time while forming pores.The composition of the electrolyte maintained in the electrolytereservoir 11 can be that of the electrolyte that was introduced into theelectrolyte matrixes during the manufacture of the fuel cells;preferably the electrolyte reservoir 11 however is filled withelectrolyte that differs from the initial composition of the electrolytein the matrixes 3 of the fuel cells 12 in order to compensatedisproportionate electrolyte losses during fuel cell operation. Thismeans that the electrolyte in the electrolyte reservoir 11 containsthose components to a higher percentage that are lost more quicklyduring fuel cell operation.

[0045] The capillary travel paths serving the distribution ofelectrolyte throughout the fuel cell stack 10 are dimensioned withregard to their thickness and/or pore size such that the electrolytetransport from the electrolyte reservoir 11 to the fuel cells 12 isoptimized so that the electrolyte quantity transported via these pathslargely corresponds to the electrolyte quantity that is lost in the fuelcells 12.

[0046] An electrolyte filling line 13, which extends outward from thefuel cell stack 10 and serves the purpose of filling the electrolytereservoir 11, is connected with the electrolyte reservoir 11. On theinside, this electrolyte filling line 13 is in contact with the porousbody of the electrolyte reservoir 11 and has an ascending or verticalcourse upward to the outside. The electrolyte filling line 13 isprovided for replenishing electrolyte, which exists in solid form atambient temperature, preferably in the form of pellets, which can befilled into filling line 13, drop into the interior of the fuel cellstack 10 and melt at the operating temperature existing there, and canbe absorbed under the effect of the capillary forces of the porous bodyforming the electrolyte reservoir 11. The quantity and frequency withwhich the electrolyte must be replenished via the filling line 13 can becalculated from experimental data and experience values in respect oftypical electrolyte loss in the affected fuel cell stack.

[0047] Since the supporting structure of the electrolyte reservoir 11preferably consists of an electrically conductive material, it can beused simultaneously for contacting the last fuel cell on the positiveend of the fuel cell stack 10, specifically for contacting the cathode 2of the fuel cell 12 located on the positive end of the fuel cell stack10. On the other end of the fuel cell stack 10 additionally acorresponding structure with a porous body, an electrolyte-absorbingreservoir 11=a for absorbing excess electrolyte, can be provided.

[0048] Pursuant to the example shown in FIG. 2, the electrolytereservoir 11 exists in a current collector 4 a, whose hollow chambersare filled with a porous body 16. This current collector 4 a is locatedbetween an end plate 6 and a bipolar plate 4 of the adjacent last cell,i.e. on the positive end of the fuel cell stack 10. A current collectoris located between the bipolar plate 4 and cathode 2 of the adjoiningcell, however for clarity reasons it is not shown in FIG. 1. Theelectrolyte reservoir on the other end of the fuel cell stack 10 can bedesigned accordingly.

[0049] Pursuant to an alternative embodiment, the hollow chambers forabsorbing a spreadable and flowing paste for the purpose of forming aporous body can also be designed as recesses or bore holes in the endplates 6, 7.

[0050] The reservoir 11 a for absorbing excess electrolyte can,preferably like the electrolyte reservoir 11, be formed by pouring aflowing mass into a current collector 4 a. For the manufacture of theelectrolyte reservoir, this mass consists e.g. of a ceramic powder (poreformation), the electrolyte material and a binding agent and/or solvent,or for the manufacture of the body absorbing excess electrolyte e.g. ofa ceramic powder (pore formation) and a binding agent and/or solvent,however not, or only to a very limited extent, of the electrolytematerial, which then only assumes the function of a high-temperatureadhesive for the ceramic particles. After curing the binding agent, thecurrent collector 4 a equipped with the electrolyte reservoir 11 can beinstalled on the positive end of the fuel cell stack 10, or theelectrolyte-absorbing reservoir 11 a absorbing excess electrolyte can beinstalled on the negative end of the fuel cell stack 10.

[0051] Information as to whether the electrolyte supply in theelectrolyte reservoir 11 is still sufficient is obtained by monitoringthe tension of the most positive fuel cell, i.e. the fuel cell which islocated on the positive end of the fuel cell stack 10 or a group of fuelcells on this end of the fuel cell stack 10, wherein a drop in tensionis used as a signal for replenishing the electrolyte supply in theelectrolyte reservoir 11 via the filling line 13. A decrease inelectrolyte in a fuel cell leads to a drop in the fuel cell tension andcan thus be interpreted as a representative signal for an electrolyteloss from the fuel cell. Since due to the electric field existing in afuel cell stack the fuel cells located on the positive end of the fuelcell stack 10 are subject to the larger electrolyte loss, the monitoringof tension of one or more cells located on the positive end of the fuelcell stack 10 is a suitable means for gaining an appropriate signal forfilling the electrolyte. Number Designation List 1 anode 2 cathode 3electrolyte matrix 4 bipolar plate 4a current collector 5 rod 6 endplate 7 end plate 10 fuel cell stack 11 electrolyte reservoir 11aelectrolyte-absorbing reservoir 12 fuel cell 13 filling line 14 gasdistributor 15 gas distributor gasket 16 porous body B fuel gas Ooxidation gas

1. Fuel cell assembly comprising a number of fuel cells (12) that arearranged in the form of a stack (10) between end plates (6, 7) andcontain, respectively, electrodes in the form of an anode (1) and acathode (2) and a porous electrolyte matrix (3) arranged between them,and contain current collectors (17) that are arranged between theelectrodes of two fuel cells (12) as well as bipolar plates (4), andcomprising an electrolyte reservoir (11) for compensating theelectrolyte losses from the fuel cells (12), characterized in that theelectrolyte reservoir (11) is provided on or in the vicinity of an endof the fuel cell stack (10) and that the electrolyte reservoir (11)consists of hollow chambers provided in the fuel cell assembly, whereinsaid chambers are formed by structures with mechanical support functioncontaining porous bodies (16) in which the electrolyte is absorbed inpores.
 2. Fuel cell assembly pursuant to claim 1, characterized in thatthe electrolyte is one component of a spreadable or flowing paste, whichis introduced into the hollow chambers, wherein additional components ofthe paste result in a porous body (16) after curing.
 3. Fuel cellassembly pursuant to claim 2, characterized in that the paste is createdby stirring powdery starting substances with a liquid binding agent. 4.Fuel cell assembly pursuant to claim 1, 2 or 3, characterized in thatthe electrolyte reservoir (11) consists of a structure, which formshollow chambers and is located between the end plate (6) and the lastcell on the positive end of the fuel cell stack (10).
 5. Fuel cellassembly pursuant to one of the claims 1 through 4, characterized inthat a current collector (4 a) is used as the structure forming thehollow chambers, as the one that is used in other areas of the fuel cellstack for current contacting.
 6. Fuel cell assembly pursuant to one ofthe claims 1 through 4, characterized in that a foam structure withmacro-pores serves as the structure forming the hollow chambers.
 7. Fuelcell assembly pursuant to one of the claims 1 through 3, characterizedin that the hollow chambers are designed in the end plates (6, 7) in theform of recesses or bore holes.
 8. Fuel cell assembly pursuant to one ofthe claims 1 through 7, characterized in that the electrolyte reservoir(11) is installed on one end of the fuel cell stack (10) and that on theother end of the fuel cell stack (10) an electrolyte- absorbingreservoir (11 a) for absorbing excess electrolyte is provided.
 9. Fuelcell assembly pursuant to claim 7, characterized in that the electrolytereservoir (11) is installed on the positive end of the fuel cell stack(10) and that the electrolyte-absorbing reservoir (11 a) for absorbingexcess electrolyte is provided on the negative end of the fuel cellstack (10).
 10. Fuel cell assembly pursuant to claim 8 or 9,characterized in that the electrolyte-absorbing reservoir (11 a) forabsorbing excess electrolyte is formed by pouring in a flowing mass,which after curing forms a porous body.
 11. Fuel cell assembly pursuantto one of the claims 1 through 10, characterized in that the electrolytereservoir (11) can be filled.
 12. Fuel cell assembly pursuant to claim11, characterized in that an electrolyte filling line (13), which isconnected with the electrolyte reservoir (11) and extends outward fromthe fuel cell stack (10), is provided for filling the electrolytereservoir (11) from the outside.
 13. Fuel cell assembly pursuant toclaim 12, characterized in that the electrolyte filling line (13) has avertical or outwardly ascending course.
 14. Fuel cell assembly pursuantto claim 12 or 13, characterized in that the electrolyte filling line(13) is provided for replenishing the electrolyte, which exists in solidform at ambient temperature, preferably in the form of pellets, whereinthe solid electrolyte at operating temperature melts in the fuel cellstack (10) and is absorbed by the electrolyte reservoir (11).
 15. Fuelcell assembly pursuant to one of the claims 1 through 14, characterizedin that the pore size of the electrolyte reservoir (11) is larger thanthat of the pores of the electrolyte matrix (3).
 16. Fuel cell assemblypursuant to one of the claims 1 through 15, characterized in that theporous body of the electrolyte reservoir (11) consists of fuel cellcathode material, which has been completely impregnated withelectrolyte.
 17. Fuel cell assembly pursuant to one of the claims 1through 16, characterized in that the structure of the electrolytereservoir (11) forming the hollow chambers consists of an electricallyconductive material.
 18. Fuel cell assembly pursuant to one of theclaims 1 through 17, characterized in that capillary travel paths forthe electrolytes existing along the fuel cell stack (10) betweenindividual components of the fuel cells (12) and/or of the fuel cellstack (10) are designed such with respect to their thickness and/ortheir pore size so as to optimize the electrolyte transport within thefuel cell stack (10) from the electrolyte reservoir (11) to the fuelcells (12).
 19. Fuel cell assembly pursuant to one of the claims 1through 18, characterized in that means for monitoring the tension ofthe most positive fuel cell (12) or a group of most positive fuel cellsare provided and that a decrease in tension is interpreted as a signalfor replenishing the electrolyte supply in the electrolyte reservoir(11).
 20. Fuel cell assembly pursuant to one of the claims 1 through 19,characterized in that the electrolyte in the electrolyte reservoir (11)is replenished in a composition that differs from the initialcomposition of the electrolyte in the electrolyte matrixes (3) of thefuel cells (12) in order to compensate disproportionate electrolytelosses during fuel cell operation.